Carbon

 Carbon can form many compounds than any other elements. 

Carbon has 4 valence electrons which can form stable covalent bonds like C-H , C-C ,C=C , C=O , C-Cl etc.

This is because :

    1. Carbon can form long chains , branched chains and rings of varying sizes. 
    

    2. Carbon can form these different arrangement because C-C, C-H bonds are strong, inert and  

        stable in the molecules.

    3. Carbon has 4 valence electrons. When carbon forms chains by forming covalent bonds with   

        another carbon, this leaves that carbon 2 other valence electrons  not bonded. 

        Then those valence electrons can form C-H, C-O,C-I,C-F,C-Cl , C-Br etc bonds by sharing 

        electrons with other atoms.

The carbon which is already forms covalent bonded with another carbon atoms can form stable covalent bonds with hydrogen , oxygen and halogens atoms.